MEDFORD - In February 1986, with the "People Power" revolt erupting in the Philippines and hundreds of thousands of protesters filling the streets of Manila, Ambassador Stephen W. Bosworth found himself confronting two famously stubborn world leaders.

One of the them, President Ferdinand Marcos, clearly had to go, but wouldn't unless his old friend and ally, President Reagan, signaled that it was time.

The other, Reagan, was intransigent in another way - not one to turn easily against a friend.

It was just the kind of dicey corner in which Bosworth, then the US envoy to the Philippines and now the dean of the Fletcher School of Law and Diplomacy at Tufts, seems at his cool and focused best.

With a flurry of adamant cables and calls, he persuaded a grudging Reagan to call for a peaceful transition to a new government. And then in a tense 3 a.m. phone call, he conveyed Reagan's decision to Marcos. Bosworth helpfully provided US helicopters for Marcos and his wife, Imelda, to flee the presidential palace.

Historians and former colleagues agree that the owlish, soft-spoken Bosworth showed the courage, the wits, and the temperament to help solve one of the most delicate crises of the Cold War era in Asia. In managing the unmanageable, he proved a virtuoso.

And now he will have to prove it again. President Obama recently named him his special envoy to North Korea, a rogue nuclear power whose leader, Kim Jong Il, is a tyrant of surpassing unpredictability and truculence. The North Koreans have scoffed at overtures from the Obama administration and yesterday, they announced that they had tested a second nuclear weapon.

"They are," Bosworth put it dryly, "very difficult interlocutors."

It is a part-time mandate; Bosworth will remain in charge at the Fletcher School. But it will demand all his diplomatic ingenuity.

US policy makers are deeply at odds over what to do about North Korea. The hermetic communist nation, led by Kim's cultish family dynasty, defied the world and exploded its first nuclear device in 2006. Last month it fired a long-range rocket over Japan, which fizzled. Two decades of intensive negotiations have broken down repeatedly in acrimony and ambiguity.

Bosworth knows North Korea like few Americans. He has dealt with the regime since the mid-1990s, when he served as the senior US diplomat in charge of implementing the Clinton administration's 1994 agreement with the North to give up its nuclear program in return for energy aid and the prospect of normalized relations with the United States. Bosworth went on to serve as US Ambassador to South Korea from 1997 to 2000.

The need now in the nation's dealings with Kim's regime, he said in an interview at his Fletcher School office, is to be rigorously clear in what we want out of the negotiations and what the North has at stake. Ambiguities must be identified and erased. It is the critical first step in what he calls the "gardening part" of diplomacy, a phrase he learned from a former boss, Secretary of State George Shultz: preparing and tending to a seed bed so it can bear fruit.

"In the broadest sense, you are trying to broaden areas of common interest and create incentives - and occasionally disincentives," he said. "You have to be clear in what you're committing to do, and what you're expecting from the other side."

He insisted that he didn't want to discuss North Korea in detail so early in his tenure and in advance of a detailed policy review. But he allowed that negotiations with the North have foundered in recent years largely because "there was a certain lack of clarity on both sides as to what the other's goals were."

One example he cited: The "agreed framework" with the North hammered out by the Clinton administration in 1994 unraveled because the US viewed it as all about denuclearizing North Korea and the North viewed it as a political deal leading toward normalized US ties.

Colleagues and admirers say that building common ground is part of Bosworth's diplomatic DNA. They point to his work as the US-appointed executive director of the Korean Peninsula Energy Development Organization, from 1995 to 1997, overseeing the 1994 accord.

"Bosworth managed to create a place where even North Koreans and South Koreans could talk to one another," said Leon Sigal, a North Korea specialist at the Social Science Research Council. Sigal recalled one event where North and South Koreans were "off in a corner . . . telling jokes to each other."

The soft touch that starts dialogue is one thing, but as Bosworth's Philippine tenure showed, he can be hard-edged when necessary.

"He's not afraid to speak out," said Morton Abramowitz, Bosworth's coauthor of numerous books and articles and a retired US diplomat. "The fact that he's reserved does not mean that he's shy or holds back. He's judicious, but he says what's necessary."

Abramowitz, then in charge of intelligence for the State Department, worked closely with Bosworth in the Philippines as well as more recently on North Korea. Abramowitz said: "In the Philippines, in those trying days, he was a pillar of strength."

Bosworth recalled the middle-of-the-night phone calls, given the time difference with Washington. "That's one of the problems being an American diplomat in Asia: You have very little uninterrupted sleep."

Bosworth last visited the North in February, just before his appointment as envoy. What he saw was disturbing. "I think it's probably a little less closed as a society than it was 14 years ago," he said, "but it's still closed."

But he was also realistic about the limits of what an outsider can truly take in.

"It's very deceptive to try to describe North Korea because you see what they want you to see," he said. "You don't wander the streets and have coffee in a sidewalk cafe. It's a very closed, regimented society."

Sigal said he worries that the Obama administration team has a number of holdovers from President Clinton's efforts on North Korea "who don't think we can get anywhere, so they don't want to do the political heavy lifting to try."

The first step, Sigal said, is to frame a policy that gives Bosworth the authority to genuinely negotiate.

"You've got to talk to North Korea," he said. "Bosworth is not about to give away the store, but he knows the only way out of this is to negotiate. Pressure tactics will never work."

Bosworth, 69, was born on a small farm in western Michigan, near Grand Rapids (and grew up a Detroit Tigers fan, though he has diplomatically joined Red Sox Nation after a stint as a Yankees fan). He combined occasional university teaching and administration stints with his diplomatic postings, teaching courses at Columbia from 1990 to 1994 and serving as Dartmouth's chairman of the board of trustees from 1996-99.

He said the Dartmouth role helped him prepare for Fletcher and for the politics of academia, which like diplomacy demands persuasion.

"In an academic institution you don't accomplish things unless you persuade constituencies that these things are worth doing," he said.

At Fletcher, Bosworth also has had to persuade faculty members, trustees, students, alumni, and other constituents to move forward with him on risky innovations. He's had demonstrable success: Fletcher has introduced three new, well-subscribed degree programs that have modernized the nation's oldest diplomatic graduate school. He is also $70 million into a $100 million fund-raising campaign.

Deborah W. Nutter, senior associate dean, has worked closely with Bosworth on many initiatives. "He doesn't waste words and he doesn't waste time," Nutter said. "He is so calm - he calms you down."

And it is true, Bosworth does seem unnaturally calm, even as he prepares to run Fletcher and tackle North Korea at the same time. "I think it's manageable. I have very good colleagues in both places," he said. As to time constraints, "What happens is that the total expands. So I'm starting earlier in the morning and finishing later at night."